We would cut this loss by more than half because a kilogram of tritium would yield about two and a half times the explosive power of plutonium. But even this advantage would soon be lost, since tritium decays at the rate of fifty per cent every twelve years, so that a kilogram produced in 1951 would decay to only half a kilogram by 1963. Plutonium, on the other hand, can be stored indefinitely without any significant loss, since it changes slowly (at the rate of fifty per cent every twenty-five thousand years) into the other fissionable element, U-235, which in turn decays to one half in no less than nine hundred million years. What is more, plutonium, if the day comes when we can beat our swords into plowshares, will become one of the most valuable fuels for industrial power, the propulsion of ships, globe-circling airplanes, and even, someday, interplanetary rockets. It holds enormous potentialities as one of the major power sources of the twenty-first century. Tritium, on the other hand, can be used only as an agent of terrible destruction. It will yield its energy in a fraction of a millionth of a second or not at all. The only other possible uses it may have would be as a research tool for probing the structure of the atom, and as a potential new agent in medicine, in which it may be used for its radiations.
How much tritium would it take to make an H-bomb 1,000 times the power of the wartime model A-bombs? Since tritium has about 2.5 times the power per given weight of U-235 or plutonium, it would take 400 kilograms (about 1,880 quarts of the liquid form) of tritium to make a bomb that would equal the power of 1,000 kilograms of plutonium. Such a bomb, we can see, would have to be made at the sacrifice of 32,000 kilograms of plutonium. In other words, we would be getting a return, in terms of energy content, of 1,000 kilograms for an investment of 32,000. And we would be losing fully half of even this small return every twelve years.
How many A-bombs would we be sacrificing through this investment? On the basis of Professor Oliphant’s estimate that the critical mass of an A-bomb is between 10 and 30 kilograms, we would sacrifice at least 1,066, and possibly as many as 3,200, if we take the lower figure. And we must not forget that a bomb a thousand times the power will produce only ten times the destructiveness by blast and thirty times the damage by fire of an A-bomb of the old-fashioned variety.
These cold facts make it clear that a tritium bomb, particularly one a thousand times the power of the A-bomb, is completely out of the picture.
But, one may ask, if a deuterium bomb is not possible and a tritium bomb is not feasible, and these are the only two substances that can possibly be used at all, isn’t all this talk about a superbomb sheer moonshine? And if so, how explain President Truman’s directive “to continue” work on it?
To find the answer let us go back for a moment to Dr. Bacher’s man in the mountains, confronted with the problem of lighting a fire with green, ice-covered wood at twenty degrees below zero with “very little kindling.” Obviously the poor fellow would be doomed to freeze to death were it not for one little item he had almost forgotten. Somewhere in his belongings he discovers a container filled with gasoline, which increases the inflammability of the wet wood to the point at which it will catch fire with a quantity of kindling that would otherwise be much too small.
Something closely analogous is true with the H-bomb. It so happens that a mixture of deuterium and tritium is the most highly inflammable atomic fuel on earth. It yields 3.5 times the energy of deuterium and about twice the energy of tritium when they are burned individually. Most important of all, the deuterium-tritium mixture, known as D-T, ignites much faster than either deuterium or tritium by themselves. For example, the D-T combination ignites 25 times faster than deuterium alone at a temperature of 100,000,000 degrees, and the ignition time is fully 37.5 times faster than for deuterium at 150,000,000 degrees.
The published technical data show that at a temperature of 50 million degrees the D-T mixture ignites in only 10 microseconds, or 20 times faster than deuterium alone. At 75 million degrees it takes only 3 microseconds, as against 40 for deuterium, while at 100 million degrees it needs only 1.2 microseconds to catch fire, a time, as we have seen, only 0.1 microsecond longer than it took the wartime A-bomb to fly apart. Since the latter held together for 1.1 microseconds at a temperature of about 50 million degrees, it is reasonable to assume that the improved and more efficient models generate a temperature at least twice as high, and that this is done by holding them together for about 1.2 microseconds.
It can thus be deduced that the only feasible H-bomb is one in which a relatively small amount of a deuterium-tritium mixture will serve as additional superkindling, to boost the kindling supplied by the improved model A-bomb, for lighting a fire with a vast quantity of deuterium. This, it appears, is the real secret of the H-bomb, which is really no secret at all, since all the deductions here presented are arrived at on the basis of data widely known to scientists everywhere, including Russia. And since it is no secret from the Russians, whom the arch-traitor Fuchs has supplied with the details still classified top secret, the American people are certainly entitled to the known facts, so vitally necessary for an intelligent understanding of one of the most important problems facing them today.
A deuterium bomb with a D-T booster would become a certainty if the temperature of the A-bomb trigger could be raised to 150 million or, better still, to 200 million degrees. At the former temperature the D-T superkindling ignites in 0.38 microseconds; at the higher temperature the ignition time goes down to as low as 0.28 microseconds. Now, the D-T mixture releases four times as much energy as plutonium, and the faster the time in which energy is released, the higher goes the temperature. Since four times as much energy is released at a rate four times faster than in the wartime model A-bomb, it is not unreasonable to assume that the temperature generated would be high enough to ignite the green wood in the bomb—its load of deuterium.